分析 Android 4.4.4 设备的 存储空间监控
在Android系统是怎样对设备存储空间进行管理和监控的呢?
如果你在使用Android手机时有过把memory填满或者即将填满的经历,也许你会注意到在这种情况下手机的Notifications栏会有“Storagespacerunningout”的通知。当点开该通知你会发现Setting–>Storage settings –>Device memory 下会有如下提示:Not enoughstorage space.
这个服务的实现是在android/framework/base/services/java/com/android/server/DeviceStorageMonitorService.java;DeviceStorageMonitorService类实现了一个监控设备上存储空间的服务。如果设备的剩余存储空间小于某一个阀值(默认是存储空间的10%,这个值可以设置)时将会向用户发送剩余空间不足的警告,让用户释放一些空间。
下面就分析一下这个类。首先看一下该服务是如何被添加进来的。在android/frameworks/base/services/java/com/android/server/SystemServer.java中使用ServiceManager.addService()来添加系统服务:
在SystemServer中添加DSMS服务:
try {
Slog.i(TAG, “Device Storage Monitor”);
ServiceManager.addService(DeviceStorageMonitorService.SERVICE,
new DeviceStorageMonitorService(context));
} catch (Throwable e) {
reportWtf(“starting DeviceStorageMonitor service”, e);
}
DSMS的构造函数的代码如下:
/**
* Constructor to run service. initializes the disk space threshold value
* and posts an empty message to kickstart the process.
*/
public DeviceStorageMonitorService(Context context) {
mLastReportedFreeMemTime = 0;
mContext = context;
mResolver = mContext.getContentResolver();
//create StatFs object
mDataFileStats = new StatFs(DATA_PATH.getAbsolutePath()); //获取Data分区信息;
mSystemFileStats = new StatFs(SYSTEM_PATH.getAbsolutePath());
//获取System分区信息;
mCacheFileStats = new StatFs(CACHE_PATH.getAbsolutePath()); //获取Cache分区信息;
//initialize total storage on device,初始化设备 总空间信息;
mTotalMemory = (long)mDataFileStats.getBlockCount() *
mDataFileStats.getBlockSize();
/*
创建4个Intent,分别用于通知存储空间不足(ACTION_DEVICE_STORAGE_LOW)、
存储空间回复正常(ACTION_DEVICE_STORAGE_OK)和存储空间满(ACTION_DEVICE_STORAGE_FULL)。
由于每个Intent都设置了FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT标志,因此这三个Intent只
能由注册了的BroadcastReceiver接收。
*/
mStorageLowIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_LOW);
mStorageLowIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
mStorageOkIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_OK);
mStorageOkIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
mStorageFullIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_FULL);
mStorageFullIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
mStorageNotFullIntent = new Intent(Intent.ACTION_DEVICE_STORAGE_NOT_FULL);
mStorageNotFullIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
// cache storage thresholds
/*
查询Seetings数据库中sys_storage_threshod_percentage的值,默认是10,即当DATA_PATH
目录下剩余空间少于其总空间的10%时,认为空间不足(ACTION_DEVICE_STORAGE_LOW)。
*/
final StorageManager sm = StorageManager.from(context);
mMemLowThreshold = sm.getStorageLowBytes(DATA_PATH);
/*
查询Settings数据库中的sys_storage_full_threshold_bytes的值,默认是1MB,即当DATA_PATH
目录下剩余空间小于等于1M时,任务空间已满,剩余的部分是保留给系统使用的。
*/
mMemFullThreshold = sm.getStorageFullBytes(DATA_PATH);
mMemCacheStartTrimThreshold = ((mMemLowThreshold*3)+mMemFullThreshold)/4;
mMemCacheTrimToThreshold = mMemLowThreshold
+ ((mMemLowThreshold-mMemCacheStartTrimThreshold)*2);
mFreeMemAfterLastCacheClear = mTotalMemory;
/*
开始检查,存储空间;
*/
checkMemory(true);
mCacheFileDeletedObserver = new CacheFileDeletedObserver();
mCacheFileDeletedObserver.startWatching();
}
================
下面再来看一下checkMemory()方法的实现。
private final void checkMemory(boolean checkCache) {
//if the thread that was started to clear cache is still running do nothing till its
//finished clearing cache. Ideally this flag could be modified by clearCache
// and should be accessed via a lock but even if it does this test will fail now and
//hopefully the next time this flag will be set to the correct value.
//如果线程 正在清除缓存CACHE_PATH ,那么不进行空间检查;
if(mClearingCache) {
if(localLOGV) Slog.i(TAG, "Thread already running just skip");
//make sure the thread is not hung for too long
long diffTime = System.currentTimeMillis() - mThreadStartTime;
if(diffTime > (10*60*1000)) {
Slog.w(TAG, "Thread that clears cache file seems to run for ever");
}
} else {
restatDataDir(); //重新计算3个分区的剩余空间大小;
if (localLOGV) Slog.v(TAG, "freeMemory="+mFreeMem);
//post intent to NotificationManager to display icon if necessary
if (mFreeMem < mMemLowThreshold) {
if (checkCache) {
// We are allowed to clear cache files at this point to
// try to get down below the limit, because this is not
// the initial call after a cache clear has been attempted.
// In this case we will try a cache clear if our free
// space has gone below the cache clear limit.
if (mFreeMem < mMemCacheStartTrimThreshold) {
// We only clear the cache if the free storage has changed
// a significant amount since the last time.
if ((mFreeMemAfterLastCacheClear-mFreeMem)
>= ((mMemLowThreshold-mMemCacheStartTrimThreshold)/4)) {
// See if clearing cache helps
// Note that clearing cache is asynchronous and so we do a
// memory check again once the cache has been cleared.
mThreadStartTime = System.currentTimeMillis();
mClearSucceeded = false;
clearCache(); //如果剩余空间低于mMemLowThreshold,先做一次缓存清理;
}
}
} else { // checkCache = false;
// This is a call from after clearing the cache. Note
// the amount of free storage at this point.
mFreeMemAfterLastCacheClear = mFreeMem;
if (!mLowMemFlag) {
// We tried to clear the cache, but that didn't get us
// below the low storage limit. Tell the user.
Slog.i(TAG, "Running low on memory. Sending notification");
sendNotification();
//如果空间仍然低于mMemLowThreshold, 发送广播并 在状态来设置一个 警告通知;
mLowMemFlag = true;
} else {
if (localLOGV) Slog.v(TAG, "Running low on memory " +
"notification already sent. do nothing");
}
}
} else { //else mFreeMem < mMemLowThreshold
mFreeMemAfterLastCacheClear = mFreeMem;
if (mLowMemFlag) { 如果 剩余空间 不小于mMemLowThreshold,且已经设置了mLowMemFlag,则 取消空间不足广播。
Slog.i(TAG, "Memory available. Cancelling notification");
cancelNotification();
mLowMemFlag = false;
}
}
if (mFreeMem < mMemFullThreshold) {
if (!mMemFullFlag) {
sendFullNotification(); //如果空间已满,则发送空间已满的广播;
mMemFullFlag = true;
}
} else {
if (mMemFullFlag) {
cancelFullNotification();
//如果 空间不满 且已经发送了空间已满的广播,则在此取消。
mMemFullFlag = false;
}
}
}
if(localLOGV) Slog.i(TAG, "Posting Message again");
//keep posting messages to itself periodically
postCheckMemoryMsg(true, DEFAULT_CHECK_INTERVAL);
//DEFAULT_CHECK_INTERVAL为1分钟,即每1分钟 会触发一次检查;
}
//mLowMemFlag和mMemFullFlag为是否发送了广播的标识。
总结:
(1)首先在构造函数中,获取data,system,cache分区信息,然后注册四个intent,分别为低内存,内存ok,内存满,内存没有满四种情况。然后获取settings数据库里的data目录下剩余空间少于其总空间的百分比值,获取数据库中data目录下剩余空间的大小临界值(用于提示用户空间已满)。然后开始检查,存储空间;checkMemory(true);
(2)
在检查存储空间时,首先判断如果线程正在清除缓存CACHE_PATH ,那么不进行空间检查。否则重新计算3个分区的剩余空间大小。如果剩余空间低于百分比10%,如果需要做缓存清理,先做一次缓存清理;清理完毕后会再次进行新一轮的checkMemory,如果剩余空间低于百分比10%并不用做缓存清理并且没有发通知,则发送通知告诉用户内部空间超出最低值10%,如果此时空间百分比正常,但已发送通知,则将通知取消。同样的,如果空间已满,大于full的临界值,则发送空间已满的广播;空间不满且已经发送了空间已满的广播,则取消。最后会每1分钟会触发一次检查空间checkMemory。
如下:清理完毕后会再次进行新一轮的checkMemory:
做一下onRemoveCompleted动作,该动作发送检查空间的消息【postCheckMemoryMsg(false, 0);这里的false就是不再执行clearCache】,然后handle处理该消息DEVICE_MEMORY_WHAT,再次进入checkMemory(false),发送通知告诉用户storage space running out,空間剩10%時會出現该提示。